AI-2 does not function as a quorum sensing molecule in Campylobacter jejuni during exponential growth in vitro

AI-2 activity was produced by the parental strain NCTC 11168 when grown in rich Mueller-Hinton broth (MHB) as expected, but interestingly was not present in defined Modified Eagles Medium (MEM-α). Consistent with previous studies, the luxS mutant showed comparable growth rates to the parental strain and exhibited decreased motility halos in both MEM-α and MHB. Microarray analysis of genes differentially expressed in wild type and luxS mutant strains showed that many effects on mRNA transcript abundance were dependent on the growth medium and linked to metabolic functions including methionine metabolism. Addition of exogenously produced AI-2 to the wild type and the luxS mutant, growing exponentially in either MHB or MEM-α did not induce any transcriptional changes as analysed by microarray.Taken together these results led us to conclude that there is no evidence for the role of AI-2 in cell-to-cell communication in C. jejuni strain NCTC 11168 under the growth conditions used, and that the effects of the luxS mutation on the transcriptome are related to the consequential loss of function in the activated methyl cycle.Campylobacter jejuni is the most common cause of food-borne diarrhoeal illness in the developed world. In 2000 there were approximately 60 000 reported cases in England and Wales [1], and there is an estimated 4 million infections (with between 200 and 1000 deaths) each year in the United States [2].In humans, Campylobacter infection causes a range of symptoms from mild, watery diarrhoea to severe, bloody diarrhoea. The illness is self-limiting but infection with certain serotypes is a common antecedent to Guillain-Barré syndrome [3,4]. Reactive arthritis also occurs in approximately 2% of C. jejuni enteritis [5,6].In many species of bacteria including enteric pathogens such as Escherichia coli, Salmonella enterica, and Vibrio cholerae, quorum sensing is thought to play a role in the expression of factors involved in diverse processes such as biofilm for